EP0318370A1 - Method for measuring the thickness of a solid deposit on the walls of a centrifuge, means for carrying out this method and its special application in the production of sugar - Google Patents

Abstract

This method consists, during rotation of the centrifugal basket (1), in applying to the surface of the layer of solids being deposited on the internal wall of this rotating basket, a sensor (9) mounted on the end of an arm (10) arranged perpendicularly to a shaft situated inside the centrifugal basket, the direction of which is parallel to that of the axis of rotation of said basket, in measuring, permanently or otherwise, the value of the angle comprised between the position occupied by said arm at a given moment or period during rotation and a position fixed in advance as reference position, and in determining the thickness "e" of said deposited layer of solids, and means for implementing the method. <IMAGE>

Description

The present invention relates to a method for measuring the thickness of a solid deposit on the walls of a centrifuge at any time during its cycle, the means for its implementation and their particular application in sugar refinery.

It will be recalled that a wringer or centrifuge is an apparatus intended to separate the solid plots from the liquid part of a heterogeneous solution in which these two constituents are intimately united.

This device uses centrifugal force to accelerate the filtration of the medium on a filter cloth capable of retaining the solid part.

A typical centrifuge (see for example Figure 1 of the accompanying drawings) comprises a cylindrical basket 1 carrying the filter cloth; the axis of this basket is secured to a motor M capable of rotating it at high speed. The basket is surrounded by a fixed cylindrical wall or "skirt" 2 intended to receive the liquid part. A cover 3 supports various accessories such as:
- inlet pipe of the mixture to be wrung,
- clearing ramp 4 (in the candy industry),
- unloading knife ...

A cone 5 is used to uniformly distribute the mass to be filtered on the filter cloth during the introduction period.

During centrifugation, the material introduced and being separated is found pressed against the internal wall of the basket 1 and forms a hollow cylinder of more or less packed material, depending on the moment considered.

It would be interesting to know the thickness "e" of this cylinder when desired, but it is difficult to determine since it is inside a closed system and this system rotates at high speed.

The object of the present invention is precisely to determine this thickness "e" of the deposited layer.

The method of the invention consists, during the rotation of the basket of the centrifuge, to apply permanently or not to the surface of the layer of solids depositing on the internal wall of this rotating basket, a probe mounted on the end of an arm arranged perpendicular to a shaft located inside the basket of the centrifuge whose direction is parallel to that of the axis of rotation of said basket, to measure permanently or not the value of the angle included between the position occupied by said arm at a given time or period (e) during rotation and a position previously fixed as a reference position and to determine the thickness "e" of said layer of deposited solids.

Under preferential conditions for implementing the process described above, the thickness "e" is calculated according to the relationship:
e = R -√b² + c² - 2bc cos (α + α _o )
where R is the radius of the basket cylinder, b , is the distance between the position of the probe and the shaft to which the arm carrying said probe is connected, c is the distance between the longitudinal axis of the basket cylinder and said shaft which it is parallel to it and α _o is the angle made by the arm carrying the probe in its reference position with the position it would have if its direction intersected the axis of rotation of the basket.

The invention also covers the means for implementing this method, these means being essentially characterized by the combination of a probe and an angle measuring transmitter apparatus, the probe comprising a shaft (6) intended to be mounted inside the basket cylinder (1) of the centrifuge and parallel to the axis of rotation thereof and bearing at one of its ends, perpendicular to it -same, an arm (10) ending in a feeler system (9) and, at the other end, systems (8) suitable for keeping said feeler in contact with the surface on which it must rest or to be called back said probe system to a given fixed reference position, said probe being associated with at least one system for determining the value of the angle (7) between said reference position (P _o ) and the working position (P) of said probe system.

According to other characteristics, said feeler system consists of a curved surface having no roughness.

According to an advantageous embodiment, the shaft (6) carrying the arm (10) and its feeler system (9) is provided at its upper end projecting outside the cover (3) of the centrifuge, a system (7) for measuring, for example a field transmitter, the value of the angle formed, possibly connected to a calculating system responsible for automatically solving the relationship recalled above and giving, by display or direct reading, the value of the desired thickness.

Other preferred means of implementing the invention described above allow the establishment of the material balance of a discontinuous centrifuge or the automatic adjustment of actions, sequential or not, depending on the thickness "e" measured. at a given time or during a period of the centrifuge cycle.

• - la figure 1 représente, comme déjà rappelé ci-dessus, le schéma d'une centrifugeuse de type clas­sique ;
• - la figure 2 représente la même centrifugeuse munie des moyens selon l'invention pour la mise en oeuvre du procédé en cause, la figure 2a étant une représentation en plan illustrant la formation de l'angle α en fonction de l'épaisseur "e" d'une couche en cours de dépôt pendant la rotation du cylindre-panier et
• - la figure 3 est une représentation, à plus grande échelle donnant la manière dont la relation ci-­dessus peut être résolue sur la base d'un raisonnement fondé sur la géométrie du système.

Other characteristics and advantages of the invention will emerge more clearly from the description which follows, given with reference to the appended drawings in which:

• - Figure 1 shows, as already recalled above, the diagram of a conventional type centrifuge;
• - Figure 2 shows the same centrifuge provided with the means according to the invention for the implementation of the process in question, Figure 2a being a plan representation illustrating the formation of the angle α as a function of the thickness "e" a layer being deposited during the rotation of the basket cylinder and
• - Figure 3 is a representation, on a larger scale giving the way in which the above relation can be resolved on the basis of a reasoning based on the geometry of the system.

Referring to these figures, the main elements constituting a centrifuge have been previously recalled in the preamble to this description and these elements will not be repeated here, the reference numbers being given in FIG. 2.

In this figure, there is shown said centrifuge illustrated in Figure 1 and the system for implementing the method according to the invention and which is constituted by the shaft 6, the latter being parallel to the longitudinal axis XY of the centrifuge; this shaft is mounted by any appropriate means and its upper end passes through the cover 3 of this centrifuge and comprises a known device called "angle measurer" 7 as well as a system called "actuator" 8 of the probe which will be discussed below. after and which is intended to urge said probe to keep it in contact with the surface of the layer of solids being deposited continuously or not.

The probe in question 9 is carried at the end of an arm 10 mounted perpendicular to the shaft 6 and at the end of the latter. This probe, according to an advantageous embodiment, may be constituted by a volume having a curved surface without roughness, so as to be able to follow at any time the face of the solid on which it must rest, whether this surface is itself constituted by the internal wall of the basket cylinder 1 or whether this surface is that of the solids deposited and then being separated from this internal wall by a distance " e "which then represents the thickness of the deposit sought.

In accordance with the invention and with reference to FIG. 2a, the angle α determined by the angle measurer 7 and formed between the two positions P _o and P of the arm 10 (P _o being the position taken as the reference position and P being the position being measured) can be used either graphically or by means of a computer (not shown).

Thus knowing the value of this angle α, we deduce the desired thickness "e" (see Figure 3). By applying the formula of any triangles, we obtain the distance "a" as a function of the known distances b and c of the angle α _o measured.

The difference R - a gives the thickness sought according to the relation:
e = R -√b² + c² - 2bc cos (α + α _o )

In the particular case of the application of the invention in the field of sweets, it may be pointed out that knowing the thickness of a wrung "e" layer, it is easy to find the volume of this layer. We find :
V = π he (De)
where h and D are respectively the height and the diameter of the basket of the wringer.

If we know the specific mass "d" of the wrung out layer, we deduce the mass contained in the basket:
P = Vd

If we know the mass of material introduced into the centrifuge, we can calculate the yield of the spinning operation immediately since we will have the result while the sugar is still in the device.

In the sugar refinery, a spin cycle includes a so-called clearing operation by which, at the end of the spin, water and / or steam is injected onto the spun sugar.

The purpose of these clearings is to clean the sugar by ridding it of the residual mother liquor. They have the disadvantage of dissolving part of the granulated sugar.

où Se = quantité de sucre entré,
et Ss = quantité de sucre sorti.We call "freinte""F" the quantity of sugar thus redissolved by clearings, compared to the quantity of sugar before clearings:

where Se = quantity of sugar entered,
and Ss = quantity of sugar released.

Since we thus have a means of knowing the volume of sugar contained in the basket during spinning, it will suffice to determine the volumes immediately before and immediately after the clearings to deduce the shrinkage.

où D = diamètre du panier de l'essoreuse.In fact, the calculation shows that it suffices to know the thicknesses e₁ and e₂ before and after clearings to determine the shrinkage "F":

where D = diameter of the wringer basket.

As a result, still in the field of sweets, the balance sheet of a crystallization workshop is simpler to carry out than by the conventional method. Indeed, this balance is usually evaluated indirectly from the percentage of dry matter (Brix) of the cooked mass to be wrung and the purities of this cooked mass and the residual sewer.

où Bmc est le pourcentage de matières sèches de la masse cuite,
Pmc est la pureté de la masse cuite,
Pe est la purete de l'égoût.The yield is then calculated by applying a formula such as, for example:

where Bmc is the percentage of dry matter in the cooked mass,
Pmc is the purity of the cooked mass,
Pe is the purity of the sewer.

It is quite obvious that, knowing directly the quantity of sugar contained in the wringer, it suffices to know the quantity of cooked mass worked to have the output.

Such an assessment can be completely automated by indicating to the computer, in addition to the angle α measured, the volume of the cooked mass introduced.

It also results from this that the quantity of clearing water can be adjusted. This quantity must be proportional to the volume of sugar to be cleared.

Usually, the quantities of water and / or steam from the clearings are fixed and adjusted manually by the opening of valves for a predetermined duration manually (of the order of ten seconds for the injection of water).

However, by measuring the thickness of the sugar layer on series of successive spin cycles, it has been found that, although it is the same cooked mass obtained continuously, the quantities of sugar obtained at each spin varies significantly.

For example, the following thicknesses were measured on a 1370 mm diameter wringer: 96.9 - 112 - 114.04 - 106.25 - 107.45 - 105.65 - 106.25 - 105.65.

The differences obtained justify considering considering adjusting the quantities of water and / or steam from the clearings to the thickness of sugar to be cleared, and this automatically.

This could be done for example as follows:

If, for a thickness "e", an injection of a duration "t" is desired, for a thickness "e ′", the injection must be of a duration "t ′" such that:

One realizes the interests and the advantage represented by the process of the invention and the means for its implementation in the conduct of a sugar campaign.

Claims (6)

1. A method of measuring the thickness of a solid deposit on the walls of a centrifuge, characterized in that it consists, during the rotation of the basket of the centrifuge, to apply, permanently or not to the surface of the layer of solids depositing on the internal wall of this rotating basket, a feeler mounted at the end of an arm arranged perpendicular to a shaft located inside the centrifuge basket whose direction is parallel to that of the axis of rotation of said basket, to measure, permanently or not, the value of the angle comprised between the position occupied by said arm at a given time or period during rotation and a position previously fixed as a reference position and to determine the thickness "e" of said layer of solids deposited. 2. Method according to claim 1, for measuring the thickness of a solid deposit on the walls of a centrifuge, process characterized in that it consists, during the rotation of the basket of the centrifuge, in applying, permanently or not, on the surface of the layer of solids depositing on the internal wall of this rotating basket, a probe mounted at the end of an arm arranged perpendicular to a shaft located inside the basket of the centrifuge whose direction is parallel to that of the axis of rotation of said basket, to measure, permanently or not, the value of the angle between the position occupied by said arm at a given time or period in during rotation and a position previously fixed as a reference position and to determine the thickness "e" of said layer of solids deposited, according to the relation "
e = R -√b² + c² - 2bc cos (α + α _o )
where R is the radius of the basket cylinder, b is the distance between the position of the probe and the shaft to which the arm carrying said probe is connected, c is the distance between the longitudinal axis of the basket cylinder and said shaft which is parallel thereto, and α _o is the angle made by the arm carrying the probe in its reference position with the position it would have if its direction intersected the axis of basket rotation. 3. Means for the implementation of the method according to claim 1 or 2, these means being essentially characterized by the combination of a probe and an angle measuring transmitter, the probe comprising a shaft (6) intended to be mounted inside the basket cylinder (1) of the centrifuge and parallel to the axis of rotation of the latter and carrying at one of its ends, perpendicular to itself, an arm (10 ) ending with a feeler system (9) and, at the other end, systems (8) suitable for keeping said feeler in contact with the surface on which it is to rest or for recalling said feeler system towards a position of fixed reference given, said probe being associated with at least one system for determining the value of the angle (7) between said reference position (P _o ) and the working position (P) of said probe system. 4. Means according to claim 3, characterized in that the feeler system (9) consists of a curved surface having no roughness. 5. Means according to one of claims 3 or 4, characterized in that the shaft (6) carrying the arm (10) and its feeler system (9) is provided at its upper end projecting outside the cover (3) of the centrifuge, of a system (7) for measuring the value of the angle formed possibly connected to a computer system responsible for automatically solving the relationship of claim 2 and giving, by display or direct reading, the value of the thickness (e) sought. 6. Means according to one of claims 3, 4 or 5 allowing the establishment of the material balance of a discontinuous centrifuge or the automatic adjustment of actions, sequential or not, depending on the thickness (e) measured at an instant given or during a period of the centrifuge cycle.

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